it has an effect, usually the opposite of what its meant to do. it doesnt give you a buzz, it does however seem to provide ur short term explosive energy supply mith more 'zest', but other than that, it just makes you feel shit (groggy, bloated, achy etc) and tired. water is good, stops headaches and you dont feel drained after 30mins.
idk i wouldn't drink it every day but i can say that when waking up at 4 in the morning after a friday night to go work on a dairy farm, energy drinks have probably saved my job